Synthesis, luminescence properties, and theoretical insights of N-alkyl- or N,N-dialkyl-pyrene-1-carboxamide

We report the synthesis and photophysical properties of N-alkyl- or N,N-dialkyl-pyrene-1-carboxamide. These derivatives, as well as pyrene, exhibited blue emission. N-Alkyl-type derivatives exhibited strong fluorescence emission (Φ_fl = 0.61 in EtOH) in both nonpolar and polar solvents. On the other hand, N,N-dialkyl-type derivatives showed weak fluorescence emission (Φ_fl <0.01) due to vibrational deactivation. However, in highly viscous solvents such as glycerin, the quantum efficiencies of N-alkyl-type (Φ_fl = 0.91) and N,N-dialkyl-type (Φ_fl = 0.082) derivatives were increased. We also investigated the fluorescence mechanism of these compounds using time-dependent density-functional theory (TD-DFT). From these results, we find that highly fluorescent pyrene-1-carboxamide derivatives can be designed by introducing an appropriate functional group at the nitrogen atom of the amide. Thus, N,N-dialkyl-type pyrene-1-carboxamide has considerable potential for use in applications such as environmental response sensors and probes.     

Synthesis and conformational analysis of N-aryl-N-(3-thienyl)acetamides

The cis-trans conformational equilibrium of amides is of interest because it can be used to control functional activity. Here, we designed and synthesized a series of N-(3-thienyl)amides in order to study the factors affecting their conformational equilibrium. NMR studies showed that the major conformer of N-methyl-N-(3-thienyl)amide in solution is the E-form (cis form), as is the case for N-methylacetamide. For N-aryl-N-(3-thienyl)amides bearing an N-phenyl moiety, the major conformers differ depending on not only the relative π-electron density of the N-aryl moiety, but also its size. X-ray analysis showed that their solid-state conformational preferences were similar to those in solution.     

Four different types of hydrogen bonds observed in 1,2-bis(N-benzenesulfonylamino)benzenes due to conformational properties of the sulfonamide moiety

The crystal structures of 1,2-bis(N-benzenesulfonylamino)benzenes with secondary and/or tertiary sulfonamide groups were determined by X-ray crystallographic analysis. Every Ar-sulfonamide group existed in synclinal conformation in the crystals even though it was secondary or tertiary. Each compound showed different types of hydrogen bonds in the crystal structure. 1,2-Bis(N-benzenesulfonylamino)benzene (1) formed two double hydrogen bonds connected to the next molecules, 1-(N-benzenesulfonylamino)-2-(N-benzenesulfonyl-N-methylamino)benzene (2) contained double hydrogen bond involved by both the sulfonamide moieties, 1,2-bis(N-4-toluenesulfonylamino)benzene (3) had both intra- and intermolecular hydrogen bonds, and 1-(N-methyl-N-4-toluenesulfonylamino)-2-(N-4-toluenesulfonylamino)benzene (4) had one double hydrogen bond involved by only one sulfonamide moiety. Sulfonamides 1 and 3 formed infinite arrays of the molecules, and sulfonamides 2 and 4 formed racemic dimer of their conformational enantiomers via the hydrogen bonds.     

Construction of macrocyclic structure using conformational properties of secondary and tertiary aromatic amides

A large macrocyclic compound with six para-phenylene rings and six amide moieties, which are alternately secondary and tertiary, was synthesized. In a stepwise synthesis, the final cyclization step was successful because a combination of three tertiary amides, which prefer a cis conformation, and two linear secondary amides would arrange both amino and carboxyl ends close to each other, while various sizes of macrocyclic compounds including the target cyclic trimer were generated in one-pot synthesis where three secondary amide bonds were formed.     

A screw-shaped alignment of pyrene using m-calix[3]amide

m-Calix[3]amide bearing three pyrenes (1a) was prepared by the condensation reaction of 3-nonylaminobenzoic acid derivative using Ph₃PCl₂. Pyrenyl groups were found to be aligned in the screw-like fashion by m-calix[3]amide as confirmed by the X-ray crystallography. Aromatic proton signals observed at the up-field region in the ¹H NMR spectrum at low temperature indicated that pyrenyl groups in 1a are aligned in close proximity in THF solution. UV–vis absorption and fluorescence emission spectra did not show marked peak shift nor concentration fluorescence quenching compared with reference compounds implying no significant electronic interaction between pyrenyl groups. These results can be explained by the steric effect of the m-calix[3]amide platform. On the other hand, an excimer emission was observed for m-calix[3]amide having a flexible spacer between pyrene and m-calix[3]amide (1b).     

Tandem synthesis of aromatic amides from styrenes in water

An expedient one-pot synthesis of aromatic amides has been reported from styrenes in the presence of N-bromosuccinimide and iodine by using aqueous ammonia in water. The reaction proceeds through the formation of α-bromoketone as an intermediate in the presence of NBS and water. α-Bromoketone on reaction with iodine forms bromodiiodoketone which on nucleophilic substitution with aqueous ammonia gives aromatic amide. Substituted aromatic amides were obtained in good yields with wide functional group compatibility.     

Stereoselective total synthesis of almorexant

A highly stereoselective synthesis of almorexant has been achieved using (R)-tert-butanesulfinamide as a chiral source. The chiral tetrahydroisoquinoline core was constructed through allylation of chiral N-sulfinyl imine followed by ring closure of the secondary amide with a tethered halide. The chiral α-phenyl amide was introduced by means of S_N2 substitution of (S)-methyl 2-phenyl-2-(tosyloxy)acetate with chiral tetrahydroisoquinoline.     

Naryl-substituted anthranilamides with intramolecular hydrogen bonds

Hydrogen bonding interaction as one type of non-covalent force has proven itself to be highly efficient for constructing structurally unique artificial secondary structures. Here, the structure of N_aryl-substituted anthranilamide in solution is demonstrated by various NMR technique, the intramolecular hydrogen bonds between amide attached to arylamine of the same ring is proposed, which is supported by its crystal structure in the solid phase. The substituent on the nitrogen atom of arylamine plays an important role in forming the presence of intramolecular hydrogen bonds. The chemical shift of the N_aryl-H downfield changes obviously, due to the formation of intramolecular hydrogen bonds and the deshielding effect of oxygen, and the neighboring C–H is activated and shows downfield protonic signal too. The presence of intramolecular hydrogen bonds probably provides the explanation for the transformation from N_aryl-substituted anthranilamide to imine, which could be converted into 2-aryl quinazolinone finally.     

A mild, expedient, one-pot trifluoromethanesulfonic anhydride mediated synthesis of N-arylimidates

The direct transformation of various secondary amides into N-arylimidates via mild electrophilic amide activation with trifluoromethanesulfonic anhydride (Tf₂O) in the presence of 2-chloropyridine (2-ClPyr) is described. Low-temperature amide activation followed by C-O bond formation with 2-naphthol provides the desired N-arylimidates in short overall reaction times. In contrast, reaction with oxindole proceeds via formation of a C-C bond to give 1-(1H-indol-2-yl)naphthalene-2-ol.     

A dipyrenyl calixazacrown chemosensor for Mg

A new fluorogenic calix[4]tetraaza-crown-6 (4) bearing two pyrene amide groups has been prepared. It was shown to be selective for Mg²⁺. When Mg²⁺ is bound to 4, the pyrene monomer emission increased while the excimer emission declined in a ratiometric manner. It is shown by ¹H NMR that this ratiometric change is due to the conformational changes of the pyrenes during the chelation of Mg²⁺ by the amide functions to form a 1:1 complex.     

Development of a generic flow-injection analysis method for compounds with a secondary amine or amide function, using an experimental design approach: Part II. Selection and evaluation of the chemical reaction parameters

A second part in the development of a generic flow injection analysis (FIA) method to determine compounds with a secondary amine or amide in their structure is described. This part consists in the selection and evaluation of the chemical reaction conditions. Sodium hypochlorite first converts the secondary amine or the amide to a primary amine. The latter reacts with o-phthalaldehyde (OPA) and a thiol (N-acetylcysteine (NAC)) to form a derivative which can be measured fluorimetrically. To investigate the influence of the different chemical reaction parameters on the peak height for a set of 31 pharmaceutical compounds, a quarter-fraction factorial design for six factors at two levels (2^6-2-resolution IV, 16 experiments) was executed. Effects on the responses were calculated for each compound. Parallel coordinate geometry (PCG) plots and principal component analysis (PCA) were also applied on the measured responses as aids in the interpretation of the results.     

The electrogenerated chemiluminescence of pyrene and some related compounds

The characteristics of the electrogenerated chemiluminescence in dimethylformamide of pyrene, 1,2-benzpyrene, 3,4-benzpyrene and dibenzo[a,lpyrene, dibenzo[a,i]pyrene, dibenzo [a,h]pyrene and dibenzo [b,l]pyrene generated with optimum conditions of applied potential are described. The appearance of emission at wavelengths longer than those expected from the excited singlet state of the hydrocarbons may be attributed to decomposition products. Pyrene and 3,4-benzpyrene exhibit long wavelength emission, however, which it is suggested may be due to excimer formation.     

Ortho-substituent effect promoted rapid cleavage of amide C–N bond under mild conditions

This article reports the ortho-substituent effect on the cleavage of the amide C–N bond. In the structure of N ^α -Phth-N-pyridinyl-amide, when the hydrogen atom in the 3-position of pyridine ring was replaced by alkoxy group, the amide C–N cleavage can take place in the 2-position of the pyridine ring. This transformation can proceed rapidly in methylamine ethanol solution under mild conditions to afford 2-amino-3-alkoxy pyridines.     

A benzthiazole-based simple receptor in fluorescence sensing of biotin ester and urea

A benzthiazole-based receptor 1 has been designed and synthesized for recognition of biotin ester and urea in CHCl₃ containing 1% CH₃CN. The receptor binds biotin methyl ester and urea with moderate binding constant values and shows significant increase in emission of benzthiazole motif. The emission characteristics of 1 upon complexation clearly distinguishes biotin methyl ester and urea from thiourea and N,N′-dimethylurea. Characterization and sensing properties of the receptor 1 were evaluated by ¹H NMR, UV-vis, and fluorescence spectroscopic methods.     

Relaxivity studies and X-ray structure of Gd(III)-diethylenetriamine-N,N′,N″-triacetic acid-N,N″-bis(2-methoxyphenethylamide) as a potential contrast agent for magnetic resonance imaging

A new bis(amide) derivative of diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (H₅dtpa), diethylenetriamine-N,N′,N″-triacetic-N,N″-bis(2-methoxyphenethylamide) (H₃L), has been synthesized. The crystal structure of gadolinium(III) complex of H₃L ([GdL]) has been determined by X-ray crystallography. The coordination sphere of Gd(III) comprises three amine nitrogens, two amide oxygens, three carboxylic acid oxygens, and one water molecule. ¹⁷O NMR shifts showed that the [DyL] complex had one inner-sphere water molecule. Relaxivity studies with the gadolinium(III) complex showed that they associate strongly with proteins leading to a significant relaxivity enhancement.     

NEW DERIVATIVES OF 4,5-BENZO-1,3,2-OXAZA (OR D1AZA)-PHOSPHOLANE FROM CONVENIENT CONDENSATION OF SUBSTITUTED UREA WITH TRIS(DIALKYLAMINO)PHOSPHINE

Abstract

The condensation of N-phenyl-N′-(2-hydroxylphenyl)urea or N-phenyl-N′-(2-aminophenyl)urea with tris(dia1kylamino)phosphine afforded derivatives of 4,5-benzo-1,3,2-oxaza (or diaza)-phospholane which formed intramolecular hydrogen bond. The cleavage of the amide bond to give N,N-dialky1-N′-phenylurea together with polymers of 1,3,2-benzodiazaphosphole was observed in the latter reaction.     

New chiral biscarboline N,N′-dioxide derivatives as catalyst in enantioselective reduction of ketoimines with trichlorosilane

New axial N,N′-dioxide secondary amide derived from l-tryptophan was synthesized and firstly employed in catalytic enantioselective reduction of ketoimines with trichlorosilane. It was found that 4f was an effective catalyst with excellent reactivity and good enantioselectivity. Possible mechanism for the catalytic procedure was tentatively proposed.     

A novel solid-phase synthesis of di- and trisubstituted N-acyl ureas

A novel, mild method for the synthesis of di- and trisubstituted N-acyl ureas on solid support is described. Addition of carboxylic acids to a resin-bound carbimidoyl chloride gave, initially, an O-acyl isourea which subsequently rearranged to the corresponding N-acyl urea. Trisubstituted N-acyl ureas were assembled on a Wang resin from a wide range of Fmoc amino acids, secondary amines and carboxylic acids. Acid mediated cleavage yielded the products in good yields and excellent purities. In addition, the regioselective synthesis of disubstituted N-acyl ureas is demonstrated with four examples.     

Acid-induced conformational alteration of cis-preferential aromatic amides bearing N-methyl-N-(2-pyridyl) moiety

A series of cis-preferential aromatic N-methyl amides was designed and synthesized, and acid-induced conformational alteration of these compounds was investigated by means of NMR measurements in solution and X-ray crystal structure analysis. Compounds with a terminal N-methyl-N-(2-pyridyl) amide unit showed acid-induced conformational change from cis to trans, while those with a terminal N-methyl-2-pyridinecarboxamide unit showed a change of the carbonyl orientation from anti to syn with retention of cis conformation.